Laboratory tests designed to expose fundamental mechanical behavior of very stiff, heavily overconsolidated soils can be difficult to interpret. Parallel testing of soil reconstituted from the matrix of the undisturbed soil therefore enables the observed behavior during testing to be assessed in a comparative way, and such effects as previous stress history, sampling, and soil fabric to be examined.

Undrained 38-mm-diameter triaxial compression testing of an Anglian till sampled undisturbed was carried out in conjunction with a soil reconstituted from its matrix. Analysis of pore pressure data showed that the critical state parameter Ac.s gave good predictions of pore pressures generated in the normally and lightly overconsolidated specimens, but tended to overestimate pore pressure in the most heavily overconsolidated specimens. It is shown that this may be accounted for by the overconsolidated specimens not reaching ultimate failure at the critical state. Parry's (1958) method of presenting pore pressure data at failure is used to construct pore pressure paths for the tills during undrained compression.